1. Field of the Invention
The present invention relates to a piezoelectric fan that blows air by using a piezoelectric element as a driving source and causing blades to vibrate.
2. Description of the Related Art
In the related art, as described in Japanese Unexamined Utility Model Registration Application Publication No. 3-35298, a piezoelectric fan that blows air by driving a piezoelectric element that is disposed on a blade, which has a flat plate-like shape, so as to cause the blade to vibrate has been designed.
FIG. 7A is an external perspective view of a piezoelectric fan 10P of the related art described in Japanese Unexamined Utility Model Registration Application Publication No. 3-35298, FIG. 7B is a plan view of the piezoelectric fan 10P, and FIG. 7C is a side view of the piezoelectric fan 10P.
The piezoelectric fan 10P includes a vibrating plate 11, piezoelectric elements 121P, 122P, 123P, 131P, 132P, and 133P, and support bodies 141 and 142. Note that, in FIG. 7, the piezoelectric elements 131P and 132P are not illustrated.
The vibrating plate 11 includes three blades 111, 112, and 113 and a base 110. The three blades 111, 112, and 113 and the base 110 are integrally formed. The blades 111, 112, and 113 are arranged along the longitudinal direction of the base 110 in the order of the blade 112, the blade 111, and the blade 113.
The piezoelectric element 121P is disposed on one of flat plate surfaces of the blade 111, and the piezoelectric element 131P is disposed on the other one of the flat plate surfaces of the blade 111. The piezoelectric element 122P is disposed on one of flat plate surfaces of the blade 112, and the piezoelectric element 132P is disposed on the other one of the flat plate surfaces of the blade 112. The piezoelectric element 123P is disposed on one of flat plate surfaces of the blade 113, and the piezoelectric element 133P is disposed on the other one of the flat plate surfaces of the blade 113.
The vibrating plate 11, which has such a configuration, is supported by being sandwiched by the support bodies 141 and 142 on the two flat plate surfaces, from the both sides of the base 110. In this case, the support bodies 141 and 142 are arranged in such a manner that an end surface of each of the piezoelectric elements 121P, 122P, 123P, 131P, 132P, and 133P and an end surface of a corresponding one of the support bodies 141 and 142 are in contact with each other.
In the piezoelectric fan 10P, the polarization direction of each of the piezoelectric elements 121P, 122P, 123P, 131P, 132P, and 133P and the direction of an applied voltage are set in such a manner that the blade 111 that is positioned in the middle in an array direction and the blades 112 and 113 that are positioned at either side in the array direction vibrate with opposite phases. Performing setting in this way allows vibration from the blade 111, which is positioned in the middle, and vibrations from the blades 112 and 113, which are positioned at either side in the array direction, to cancel each other out on the support bodies 141 and 142. Consequently a vibration in the support bodies 141 and 142 is suppressed.
However, in the piezoelectric fan 10P, which has the configuration described in Japanese Unexamined Utility Model Registration Application Publication No. 3-35298, the following problems occur. FIG. 8 is an enlarged plan view for describing problems concerning the piezoelectric fan 10P, which has the configuration described in Japanese Unexamined Utility Model Registration Application Publication No. 3-35298
In the piezoelectric fan 10P described in Japanese Unexamined Utility Model Registration Application Publication No. 3-35298, as described above, the support bodies 141 and 142 are arranged such that the end surface of each of the piezoelectric elements 121P, 122P, 123P, 131P, 132P, and 133P and the end surface of the corresponding one of the support bodies 141 and 142 are in contact with each other. However, in practice, a gap may sometimes be generated between the end surface of each of the piezoelectric elements 121P, 122P, 123P, 131P, 132P, and 133P and the end surface of the corresponding one of the support bodies 141 and 142 due to errors in mounting the piezoelectric elements 121P, 122P, 123P, 131P, 132P, and 133P and the support bodies 141 and 142 onto the vibrating plate 11 or the like.
For example, as illustrated in FIG. 8, there is a case where a gap Gap1 is generated between the piezoelectric element 121P and the support body 141, a gap Gap2 is generated between the piezoelectric element 122P and the support body 141, and a gap Gap3 is generated between the piezoelectric element 123P and the support body 141. In this case, the resonant frequencies of the blades 111, 112, and 113 will be different from one another unless the widths of the gaps Gap1, Gap2, and Gap3 match one another.
Table 1 shows examples of the resonant frequencies of the blades 111, 112, and 113 in the case where the widths of the gaps Gap1, Gap2, and Gap3 are different from one another. Table shows the resonant frequencies at each of which a corresponding one of the blades 111, 112, and 113 of the piezoelectric fan 10P of the related art can obtain a maximum amplitude.
TABLE 1Piezoelectric Fan 10P(Related Art)Resonant FrequencyLeft Blade 11265.5[Hz]Middle Blade 11168.5Right Blade 11367.5
As shown in Table 1, in the case where the widths of the gaps Gap1, Gap2, and Gap3 are different from one another, and where the resonant frequencies of the blades 111, 112, and 113 are different from one another, when driving signals of the same frequency are applied to the blades 111, 112, and 113, the amplitudes of the blades 111, 112, and 113 are different from one another.
Table 2 shows examples of amplitudes of the blades 111, 112, and 113 in the case where the widths of the gaps Gap1, Gap2, and Gap3 are different from one another, and where driving signals of the same frequency are applied to the blades 111, 112, and 113. The frequency of an applied voltage is the average value of the resonant frequencies of the blades 111, 112, and 113. Note that the ratio of residual vibration shown in Table 2 is an index that indicates the ratio of the residual vibration that has not been canceled out to the average value of the amplitudes of the blades 111, 112, and 113. The specific method of calculating the ratio of residual vibration will be described later.
TABLE 2Piezoelectric Fan 10P(Related Art)Frequency of Applied Voltage [Hz]67.0AmplitudeLeft Blade 1125.3[mm]Middle Blade 1115.2Right Blade 1135.9Average Amplitude [mm]5.4Ratio of Residual Vibration [%]3.7
As shown above, in the case where the amplitudes of the blades 111, 112, and 113 are different from one another, when propagating to the support bodies 141 and 142, the vibrations from the blades 111, 112, and 113 cannot cancel one another out, and the vibration in the support bodies 141, 142 cannot be suppressed.
Note that this phenomenon occurs not only in the case of a structure in which three blades are used but also in the case of a configuration in which a plurality of blades are used.